NEW YORK — An acne skin cream prescribed for teen-agers may spur cell growth in aged skin, a University of Pennsylvania researcher said Monday this week.

Dr. Albert Kligman, a professor of dermatology at the school, said the skin of 28 elderly women in a Pennsylvania nursing home became thicker and more elastic after topical applications of cream containing the drug retinoic acid.

He said biopsies showed the drug increased the number of skin cells and the amount of collagen, a fibrous protein that gives skin elasticity.

Retinoic acid, a derivative of vitamin A, has been used in the treatment of acne, which afflicts mainly adolescents and young adults, for the past 15 years.

``We did before and after biopsies of the skin,`` said Kligman, adding that his findings would be presented in medical journals within a few months. ``We saw an increase in the thickness of the skin. The fibroblasts were definitely producing more collagen.``

However, Kligman said he did not know how the drug worked.

``Retinoids appear to stimulate cell reproduction,`` he said. ``I`m just describing what I see. Nobody knows.``

In clinical trials, half of 32 women in the nursing home received a daily application of retinoic acid to a patch of skin on their forearms for six months and the other half received a cream without the drug, he said.

Another 12 women in the home received twice daily applications of the drug to their faces for three months.

The epidermis of the 28 women who received the drug increased in thickness by an average of 40 percent, said Kligman. He said biopsies of these women also showed increased collagen in their skin and an increase of the flow of blood through the dermis.

For years, dermatologists have shunned creams as a treatment for aged skin because ingredients in the creams cannot enter the dermal, or lower, layers of the skin.

Kligman said he believes the retinoic acid enters the dermis because the molecules of the drug are very small and are soluble in the skin`s fat.